1. Field of the Invention
The present invention relates to a disc apparatus capable of recording a signal in a medium such as an optical disc with a laser beam applied from an optical pickup device or capable of reproducing a signal recorded in a medium such as an optical disc with a laser beam.
2. Description of the Related Art
A laser beam applied from an optical pickup device (OPU) of an optical disc apparatus is focused on a signal surface of an optical disc. Laser (LASER) is an abbreviation for “light amplification by stimulated emission of radiation”. A technology of focusing the laser beam on the signal surface of the optical disc, so-called focusing control technology includes various types. In general, the focusing control is performed by utilizing a signal obtained through a photodetector included in the optical pickup device.
A focus means a focal point or focal spot, for example. Focusing means bringing into focus or coming into focus. Defocus adjustment in this description means an adjustment operation of focusing for an object out of focus, for example.
According to specifications in which the focusing control is described, for example, there are described a focusing controlling apparatus and a focus pull-in method, where a focus pull-in operation is certainly performed in a short period of time for an optical disc with reflectance varying depending on sates or a phase change optical disc with reflectance varying due to heat of applied light (see, e.g., Japanese Patent Application Laid-Open Publication No. 2002-342948 (pages 1, 3 to 5, FIGS. 1 to 5)).
The focusing control is generally performed by a circuit called a focusing servo circuit and the displacement operation of an objective lens is performed based on a position that is the center of the operation of the objective lens, for example. A servo means, for example, those including a mechanism performing automatic correction control with measuring a state of a control target to be compared with a predetermined reference value.
For example, some optical pickup devices include a system where an arbitrary offset (OFFSET) can be applied by a focus mechanism, and jitter (jitter) is adjusted at the time of reading data from a disc (DISC) based on focus offset (FOCUS_OFFSET) that is the so-called defocus (DEFOCUS). The jitter means slight fluctuation and distortion of a signal, for example.
For example, in some optical pickup devices, a jitter value included in a signal such as a reproduction signal is detected to adjust the operational center position of the objective lens (see, e.g., Japanese Patent Application Laid-Open Publication No. Hei7-262584 (pages 1 and 2, FIGS. 1 to 6)).
In optical pickup devices, an F-bias (F BIAS) value, which is a bias (BIAS) value of the focus (FOCUS), so-called defocus value, is rendered variable so that the defocus value is set at the optimum jitter value.
For example, in some optical disc reading apparatuses, there can be obtained a focus bias amount corresponding to an optical disc by detecting a correlation between a focus bias value displacing a reference position of the focus of a pickup and a jitter value of data read by the pickup (see, e.g., Japanese Patent Application Laid-Open Publication No. 10-228652 (pages 1 and 2, FIGS. 1 to 8)).
The focusing control in the optical disc apparatus is performed with the use of a focusing error signal obtained by the photodetector. If the objective lens is displaced substantially in a direction orthogonal to a surface of the optical disc by the focusing control, a focusing error signal called S-shaped curve can be obtained as described in patent document 1, for example. If the level of the focusing error signal falls within a focusing controllable range in which a point called zero-cross of the S-shaped curve is the center, the focusing servo operation is performed to execute the focusing control. By performing the focusing servo operation, a laser beam applied from a laser diode is focused on the signal surface of the optical disc.
A technology of setting a focal point of a laser beam on a substantially spiral track provided on a signal surface of an optical disc, so-called tracking control technology includes various types. In general, the tracking control is performed by utilizing a signal obtained through the photodetector included in the optical pickup device.
In this description, a track means a track of signal in an optical disc, for example. Tracking means tracking a micro signal portion provided on the signal surface of the optical disc with the use of light to set a position on a substantially spiral-shaped track.
According to specifications in which the tracking control is described, for example, there are described a rotation correction circuit, a semiconductor integrated circuit, an optical disc device, and a rotation correction method, which: achieve a good information data reading performance even at the time of high-speed rotation of an optical disc with eccentricity or wobbling; and are able to stably execute track jumps and layer jumps (see, e.g., Japanese Patent Application Laid-Open Publication No. 2003-263760 (pages 1 and 5, FIGS. 1 to 29)).
The tracking control is generally performed by a circuit called a tracking servo circuit and the displacement operation of the objective lens is performed based on a position that is the center of the operation of the objective lens, for example.
For example, some optical pickup devices include a system where an arbitrary offset (OFFSET) can be applied by a track mechanism, and jitter (jitter) is adjusted at the time of reading data from a disc (DISC) based on track offset (TRACK_OFFSET) that is the so-called detrack (DETRACK).
In optical pickup devices, a T-bias (T BIAS) value, which is a bias (BIAS) value of the track (TRACK), so-called detrack value, is normally rendered variable so that the detrack value is set at the optimum jitter value.
For example, there has been devised an optical disc apparatus that invariably sets a track bias amount with calculation processes. For example, there has been also devised an optical disc apparatus that sets a track bias amount based on the minimum jitter value.
In conventional optical disc apparatuses including a tilt mechanism or tilt function, correction of skew in a radial direction of a disc (disc) and correction of recording quality are facilitated. The tilt (tilt) in optical disc apparatuses or optical pickup devices means angle deviation between a disc surface and a light axis of the objective lens. The skew (skew) means “deformation” and “bending”.
For example, some optical pickup devices include a system where an arbitrary offset (OFFSET) can be applied by a tilt mechanism, and to adjust jitter (jitter) is adjusted at the time of reading data from a disc (DISC) based on tilt offset (TILT_OFFSET) that is the so-called tilt (TILT).
The above apparatuses provided with the tilt function include an optical head device not requiring addition of power feeding wires to a lens holder and not causing increase in size and weight of the lens holder (see, e.g., Japanese Patent Application Laid-Open Publication No. 2002-197698 (pages 1 and 2, FIGS. 1 to 3)).
In optical pickup devices, a tilt value is normally rendered variable so that the tilt value is set at the optimum jitter value. For example, there has been devised an optical disc apparatus that invariably sets a tilt bias amount with calculation processes. For example, there has been also devised an optical disc apparatus that sets a tilt bias amount based on the minimum jitter value.
In the above optical pickup device, there is a problem that a focus position obtained by control of the focusing servo operation is not always the best focal point due to an individual difference of an optical pickup device itself or an optical disc, so that the focusing servo operation is not performed in the optimum state.
To solve the above problem, for example, there has been proposed an optical disc reading apparatus described in the patent document 3. However, in an optical disc reading apparatus described in Japanese Patent Application Laid-Open Publication No. 10-228652, for example, since the focus bias amount is set through a calculation process, the time required for the setting process is prolonged, which may be a problem.
For example, when performing a method of setting the focus bias amount based on the minimum jitter value, the following problems may occur. For example, among optical discs to be used, there are optical discs for which jitter value changes very slightly. A bias amount set in the case of such an optical disc may be a focus bias amount at the edge of detection range. When the focus bias amount is set in this way, the focusing servo operation becomes unsteady, which is a problem.
Specifically, in some optical discs, a jitter value corresponding to a defocus value may not substantially be changed when the defocus value is adjusted by the optical pickup device, or a jitter value enabling steady reading operation is obtained even if a defocus value is set to zero. If a biased defocus value is set in accordance with the optimum jitter for such optical discs, the servo becomes unsteady due to this defocus value, resulting in focus drop, so-called F-drop, etc.
The focus drop means, for example, that a focus of a laser beam emitted from an optical pickup device deviates from a pit portion of a disc in a state of being tracked, so that data recorded in the disc becomes unable to be read. A pit means a hole or a dent portion.
For example, when the defocus adjustment is performed based on the detected jitter, the F-drop may occur in an optical pickup device having slight changes in jitter. When the defocus adjustment is performed in an optical pickup device having slight changes in jitter, a defocus value may be set at a value apart from the center value corresponding to the center of the operation of the objective lens. If such a setting is performed, the F-drop may occur in the optical pickup device.
When the defocus adjustment is performed in an optical pickup device, if a value other than zero is set as the defocus value, a problem occurs that a track may not be caught when the optical pickup device performs a track jump on an optical disc.
In the conventional optical pickup device, there is a problem that a focus position obtained by control of the tracking servo operation is not always the best focal point due to an individual difference of an optical pickup device itself or an optical disc and, so that the tracking servo operation is not performed in the optimum state.
For example, in the optical disc apparatuses setting the track bias amount through a calculation process, since the track bias amount is set through a calculation process, the time required for the setting process is prolonged, which may be a problem.
For example, when performing a method of setting the track bias amount based on the minimum jitter value, the following problems may occur. For example, among optical discs to be used, there are optical discs for which jitter value changes very slightly. A bias amount set in the case of such an optical disc may be a track bias amount at the edge of detection range. When the track bias amount is set in this way, the tracking servo operation becomes unsteady, which is a problem.
In some optical discs, a jitter value corresponding to a detrack value may not substantially be changed when the detrack value is adjusted by the optical pickup device, or a jitter value enabling steady reading operation is obtained even if a detrack value is set to zero. If a biased detrack value is set in accordance with the optimum jitter for such optical discs, the servo becomes unsteady due to this detrack value, which may result in track skip, etc.
The track skip means, for example, that a focus of a laser beam emitted from an optical pickup device deviates from a track portion of a disc in a state of being tracked, so that data recorded in the disc becomes unable to be read.
For example, when the detrack adjustment is performed based on the detected jitter, the track skip may occur in an optical pickup device having slight changes in jitter. When the detrack adjustment is performed in an optical pickup device having slight changes in jitter, a detrack value may be set at a value apart from the center value corresponding to the center of the operation of the objective lens. If such a setting is performed, the track skip may occur in the optical pickup device.
When the detrack adjustment is performed in an optical pickup device, if a value other than zero is set as the detrack value, a problem occurs that a track may not be caught when the optical pickup device performs a track jump on an optical disc.
In the conventional optical pickup device, there is a problem that a focus position obtained by control of the focusing servo operation is not always the best focal point due to an individual difference of an optical pickup device itself or an optical disc, so and that the tilt operation is not performed in the optimum state.
For example, in the optical disc apparatuses setting the tilt bias amount through a calculation process, since the tilt bias amount is set through a calculation process, the time required for the setting process is prolonged, which may be a problem.
For example, when performing a method of setting the tilt bias amount based on the minimum jitter value, the following problems may occur. For example, among optical discs to be used, there are optical discs for which jitter value changes very slightly. A bias amount set in the case of such an optical disc may be a tilt bias amount at the edge of detection range. When the tilt bias amount is set in this way, the tilt operation becomes unsteady, which is a problem.
In some optical discs, a jitter value corresponding to a tilt value may not substantially be changed when the tilt value is adjusted by the optical pickup device, or a jitter value enabling steady reading operation is obtained even if a tilt value is set to zero. If a biased tilt value is set in accordance with the optimum jitter for such optical discs, the servo becomes unsteady due to this tilt value, resulting in servo failure, etc.
For example, when the tilt adjustment is performed based on the detected jitter, the servo failure may occur in an optical pickup device having slight changes in jitter. When the tilt adjustment is performed in an optical pickup device having slight changes in jitter, a tilt value may be set at a value apart from the center value corresponding to the center of the operation of the objective lens. If such a setting is performed, the servo failure may occur in the optical pickup device.
When the tilt adjustment is performed in an optical pickup device, if a value other than zero is set as the tilt value, the servo failure tends to occur when the optical pickup device performs a track jump on an optical disc, which is a problem.